RS-485 Port Protection
Evaluation Board 1
Introduction
This Evaluation Board serves as an aid in
evaluating circuit protection on RS-485
serial device ports, using two Bourns®
TBU® High-Speed Protectors (HSP), two
fast-acting GDTs and two TVS diodes to
meet the required industry standards on
RS-485 port interfaces. The recommended
Bourns® TBU® device solution, with a
low capacitance GDT, offers enhanced
high-speed performance features over
competing technologies, which can help
the design engineer increase the surge and
transient protection level on RS-485 ports
and place the entire circuit protection
solution into a smaller reduced PCB
area. Bourns has developed an RS-485
Evaluation Board (measuring 45 mm x
21 mm x 1.2 mm) manufactured using FR4
PCB with nickel gold plating on the top
and bottom sides.
TBU® HSP 1
1
1
1
2
1
IN1
1
GDT1
2
3
2
TVS1
1
TVS3
1
3
2
2
3
1
2
OUT1
1
GDT3
2
2
2
TVS5
3
1
GND
GND
1
GDT2
1
TVS2
1
2
1
TVS4
1
OUT2
IN2
TBU® HSP 2
Figure 1
RS-485 Evaluation Board Schematic
How to Connect the Evaluation
Board for Test Set-up
• Connect IN1 and IN2 to the
exposed lines.
• Connect OUT1 and OUT2 to the
RS-485 IC device.
* The default configuration of this board uses 2 GDTs
(GDT1, GDT2) and discrete SMB TVS diodes
(TVS1,TVS2). The board allows different configurations:
• 2 single 2031 GDTs (GDT1 and GDT2) may be
replaced by a dual 2030 GDT (GDT3)
• 2 SMB TVS diodes (TVS1 and TVS2) may be
replaced with a) 2 SOT23 TVS diodes (TVS3, TVS4)
or b) a single TVS diode array (TVS5)
Figure 2
RS-485 Evaluation Board Top Side Layout*
Table 1
RS-485 Evaluation Board Bill of Materials
No.
1
2
3
Part Number
TBU-CA065-200-WH
2031-23T-SM-RPLF
SMBJ12CA
Qty.
2
2
2
Description
TBU® Single Bidirectional Line 650 V 200 mA
Single Line Fast-acting GDT 650 V
Single Bidirectional Line TVS 12 V SMB
1
Reference
TBU® HSP 1, TBU® HSP 2
GDT1, GDT2
TVS1, TVS2
10/12 • FU1213
RS-485 Port Protection Evaluation Board 1
Performance Graphs
Run
T
T
Trig’d
PreVu
T
T
Trig?
1
Ch1 RMS
126.7 V
2
Ch4 Max
371.2 mA
Ch4 Min
-359.9 mA
1
Ch1 Max
508 V
4
4
Ch4 Max
1.74 A
Ch1
200 V
Ch2
Ch4
20.0 V
M 2.00 ms A
Line
200 mAΩ
T
27.20 %
-3.98 V
Ch1
200 V
Ch4
1.00 AΩ
M 200 ns
T
31.00 %
A
Ch1
-172 V
Ch 1: AC power generator
Ch 2: Voltage on protected side of world (downstream
of TBU® device at SMBJ12CA TVS diode side)
Ch 4: Current consumed (TBU® HSP trigger current)
The ohm unit following the current units
shown for Channel 4 (i.e. AOhm)
indicates that a 50 ohm termination was
used internal to the oscilloscope
Ch 1: Surge generator
Ch 2: Consumed current (TBU® HSP Trigger current)
Note: The noise generated by the GDT when it fires
causes a ground bounce and is reflected in current
measurement at the time the GDT device is triggered.
The ohm unit following the current units
shown for Channel 4 (i.e. AOhm)
indicates that a 50 ohm termination was
used internal to the oscilloscope
Figure 3
Power Cross 120 V
rms
Figure 4
Slew Rate 1 KV/µs
PreVu
T
T
Reference
For more information on implementing advanced circuit
protection technologies for RS-485 ports, please review the
Bourns® RS-485 application note:
http://www.bourns.com/data/global/pdfs/bourns_cpk1047_
rs485_circuit_protection_appnote.pdf
1
Ch1 Max
625 V
Ch4 Max
1.64 A
4
Ch1
200 V
Ch4
1.00 AΩ
M 200 ns
T
30.40 %
A
Ch1
312 V
Ch 1: Surge generator
Ch 2: Consumed current (TBU® HSP Trigger current)
Note: The noise generated by the GDT when it fires
causes a ground bounce and is reflected in current
measurement at the time the GDT device is triggered.
The ohm unit following the current units
shown for Channel 4 (i.e. AOhm)
indicates that a 50 ohm termination was
used internal to the oscilloscope
For further technical support
and for complete circuit protection solutions,
please visit
Figure 5
Slew Rate 5 KV/µs
www.bourns.com
10/12 • FU1213
“TBU” is a registered trademark of Bourns, Inc. in the U.S., Taiwan and European Community.
“Bourns” is a registered trademark of Bourns, Inc. in the U.S. and other countries.
COPYRIGHT© 2012 • BOURNS, INC. • 10/12 • e/FU1213
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
